The 72-year-old comedian was diagnosed with the brain condition in 2012 - in the same week he was told he had prostate cancer and had two hearing aids fitted - and although it has prevented him from playing the banjo he doesn't dwell on the degenerative impacts.

He said: ''I am doing as well as can be expected. Some people get grim, but I do not.

''Funny doesn't go away it just changes slightly, maybe some people get grim but I don't. I think it is an attitude - you say screw it, let's get on with it.

''You cannot sit at home wondering about your symptoms. It is not going to go away.

''It has never crossed my mind that I am gonna die. What is dying anyway? It is just a light going out?''

'The Hobbit: The Battle of the Five Armies' actor admitted the disease is a constant reminder of his late friend Robin Williams who had the same condition before committing suicide.

During a radio interview promoting his Canadian tour, he explained: ''It depressed me terribly. You don't find a way out of it. You find a place to put it where you can access when you want it. Like your mother or father's death you never get over it, you just find a place to put it.

''We were both angry about things.

''For instance the guy who gave me the final diagnosis that I had Parkinson's said it was incurable. Now I think that is terrible; he should have said we have yet to find a cure ... Leave me a little light on in the corner for Christ's sake.''